Added the skeleton for changing the sky to the blank sky image

Once sky image is loaded and comments are replaced with correct code, clicking ground will toggle a blank deer, clicking the sky will toggle a blank sky.

Next Steps: 
+ figure out the best way to determine where the cursor is (how to define range for deer? an array of ranges? a really complicated if-else statement?)
+ add a simple animation after clicking (the lines in the sky flicker out? maybe add the bird flying out of the crack in the cardboard when the deer turns blank?)